This invention relates generally to a flow control system for use in an actuator and, in particular, to a flow limiter for use in conjunction with a control valve in an actuator control system.
Actuators are used in motion simulators to control the motion of a load under simulation. Typically, the actuator will include a drive cylinder that houses a piston and a piston rod which connects the piston to the load. Fluid is routed from one side of the piston to the other by means of a control valve to either extend or retract the piston rod and thus move the load. Typically, the simulator will employ a plurality of actuators that work together to simulate a full range of complex movements. During motion simulation, the actuators generally are moving at different velocities and the actuator rods are moving in different directions.
One of the major problems associated with motion simulators is the overspeeding of the load as the actuator is being extended. This is caused by the inertia of the load or when the stress on the rod changes dramatically from compression to tension because of the offsetting of the load. In order to prevent overspeeding, a flow limiter is placed in the flow control line in series with the control valve of each actuator to limit the rate of fluid flow that can be returned by the control valve to the back side of the actuator piston. Most prior art flow limiters, however, have been found to be unacceptable for use in this type of control system primarily because they produce an unacceptable pressure loss in the flow circuit which adversely effects the performance of the associated control valve and the operation of the actuator. Furthermore, most prior art flow limiters are designed to handle flows in one direction only. The flow of fluids through these devices in a reverse direction is usually restricted, which again seriously effects the operation and performance of the overall system. Turner et al., in U.S. Pat. No. 3,630,228, discloses a flow regulator for providing a constant rate of flow in a jet engine water injection system. Here, the flow of fluid is in one direction only. Turner et al. employs a piston and control spring mechanism to open or close a throttling valve in response to changes in pressure sensed over an orifice placed in the flow stream. The control spring is positioned in the flow immediately adjacent to the sensing orifice while the throttling valve is some distance away. The spring produces an unwanted restriction in the flow and also acts as an uncontrolled orifice that adversely effects the performance of the device. The response of the Turner et al. device is also relatively slow because of the remote positioning of the throttling valve in regard to the sensing orifice. As a consequence, the performance of the device under certain operating conditions can change as the throttle attempts to adjust to changes in flow conditions.